The present invention relates to a private branch exchange having a caller number informing function and a caller number information restricting function or having a connected party number informing function and a connected party number information restricting function.
In an integrated services digital network (ISDN), a caller number informing function and a called number information restricting function are defined, and a private branch exchange having a function of informing a caller number has already been developed. The caller number informing function is provided so that a called party can identify the calling party and, if necessary, can call back with use of the informed caller number. In the public integrated services digital network (ISDN), too, the caller number provided along with a call setting signal at the time of calling is verified on condition that a callback can be made. If the caller number is determined to be improper in the verification by the network, the improper caller number is replaced with a proper caller number and transmitted to the destination apparatus. In the network, caller numbers are managed in units of an interface (i.e., an office line or a plurality of office lines capable of being controlled by one control channel).
In order to carry out the caller number informing function, a data structure, for example, as shown in FIG. 1, is adopted. In FIG. 1, whether or not the caller number is informed is determined as follows. A caller number information element identifier in OCTET1 (8-bit data) is referred to in order to determine whether there is data on the caller number. If there is the caller number data, the caller number data is read from OCTET4. In this manner, the caller number is informed to the called party. The caller number data in OCTET4 is character-string data.
The caller number informing function will be further described. FIG. 2 schematically shows a process 40 for the caller number in the conventional private branch exchange. A call signal 41 from an extension may be an analog signal or a digital signal, depending on the type of the extension. On the basis of a caller number 42 associated with the extension held within the private branch exchange, a process 43 for associating the caller number 42 with the call signal is performed. A call signal 44 to the network is termed xe2x80x9ccall settingxe2x80x9d in the integrated services digital network and it includes the caller number 45. The counter-side terminal 46 receives a call via the integrated services digital network and includes a display 47.
In FIG. 2, if the private branch exchange has received the call signal 41 from the extension, it associates the call signal 41 with the caller number 42 stored therein and corresponding to the extension. When the private branch exchange sends the call signal 44, it incorporates the caller number 45 into the call signal 44. The destination apparatus 46 which has received the call displays the caller number on the display 47 and identifies the caller. Using this number, a callback is made. In a case where the extension is one matching the integrated services digital network, the caller number may be contained in the call signal 41 and informed from the extension.
According to standards or recommendations specifying the protocols of the integrated services digital network, it is verified by the network, from a standpoint of security, whether the caller number 45 coincides with a contractual number. If the caller number does not coincide, it may be replaced with the contractual number on the network.
On the other hand, a service called xe2x80x9cdirect dial-inxe2x80x9d is provided, wherein if a callback is made or a general call is received from the network, the extension for the call reception is determined on the basis of the content of the called number information element included in the call setting signal for the call reception.
FIG. 3 schematically shows a direct dial-in process 50 in the conventional private branch exchange. A called number conversion table 51 converts the called number to the extension number in order to carry out the direct dial-in. The called number conversion table 51 is provided for each interface (an office line or office lines controllable by one control channel). The call reception signal 52 from the network is termed xe2x80x9ccall settingxe2x80x9d in the integrated services digital network and includes the called number 53. The called number conversion table 51 is searched on the basis of the called number 53, and the extension number 54 of the called party is obtained. The call reception signal 55 to the extension number 54 may be an analog signal or a digital signal, depending on the kind of the extension.
In FIG. 3, if the call reception signal 52 is received from the network, the private branch exchange obtains the extension number 54 of the called party on the basis of the called number 53 included in the private exchange, with use of the called number conversion table 51 provided within the exchange. Then the private branch exchange sends out the call reception signal 55. Thereby, the call is connected to the extension corresponding to the called number.
In general, the private branch exchange accommodates more extension terminals than called numbers which can be received from the network. Thus, all extensions are not assigned called numbers, nor can automatically receive calls. There are many extension terminals which cannot directly receive calls from the integrated services digital network.
When such an extension transmits a call with use of the integrated services digital network, a callback cannot be made. Thus, the caller number information element which can identify the extension cannot be sent to the network. In such a case, the caller number is supplemented by the network. In the case of the private branch exchange, however, no callback can be made to the extension, which actually transmitted the call, with the supplemented number. In this case, a caller number presentation restriction should have been sent to the network to prevent the counter-side terminal from being provided with the caller number, but this is not done.
Moreover, in general, in the private branch exchange having the function of informing the caller number, the caller numbers permitting callback are preset in the extension terminal or in the private branch exchange. In the private branch exchange, in a case where the extension always selects a specified office line to make a call, if the caller number is properly set, the call passes the network verification and reaches the counter-side terminal. It is usual, however, in the private branch exchange that use is made of an office line selection function for selecting a most inexpensive office line or selecting a non-busy office line when a certain office line is busy. In this case, if the extension issues a call by selecting an office line different from an ordinary one, the caller number which is proper in the ordinarily selected office line is determined to be improper in the different office line by the network verification. As a result, a default number in the network is supplemented and transmitted to the counter-side terminal.
As stated above, in the conventional private branch exchange, it is difficult to easily inform the caller number with which a callback can actually be made. If the office line selection function is used, the number, which is proper in ordinary cases, may become improper. It is very difficult to take such flexible measures as informing the caller number with which a callback can actually be made, or sending a caller number presentation restriction to the network in a case where the proper caller number cannot be informed.
In the conventional private branch exchange, as described above, services have not been informed from the standpoint as to whether or not a callback can be made, when the caller number is informed or the presentation restriction is sent. There is a concern that a caller number, with which a callback cannot be made, is informed to the counter-side party.
The object of the present invention is to provide a private branch exchange capable of informing a caller number with which a callback can actually be made, or positively informing a caller number presentation restriction to the network when the caller number with which the callback can actually be made cannot be informed, thereby preventing the network from supplementing a caller number which is invalid for the callback.
A private branch exchange according to the present invention comprising: means, including at least an extension terminal, for connecting the extension terminal to a communication network; means for transmitting to the communication network a call including information relating to a caller number, when a transmission call is made from the extension terminal; means for sending, when a call is received from the communication network and the call includes information on a number, the call to the extension terminal corresponding to the called number; memory means for storing information on a predetermined number which is preconfirmed to function as a called number for callback; determination means for determining, when a call has been received from the extension terminal, whether or not the predetermined number is obtained, which corresponds to a caller number received from the extension terminal or a caller number corresponding to the extension number, with use of the information stored in the memory means; and means for employing, when the acquisition of the called number has been determined by the determination means, the predetermined number as a caller number and transmitting transmission call information including information relating to the caller number to the communication network. The same structure may be adopted in a case where the extension terminal has responded to a reception call. Specifically, a private branch exchange comprising: means, including at least an extension terminal, for connecting the extension terminal to a communication network; means for transmitting to the communication network a call including information relating to a connected party number, when the extension terminal has responded to a reception call; means for sending, when a call is received from the communication network and the call includes information on a reception number, the call to the extension terminal corresponding to the called number; memory means for storing information on a predetermined number which is preconfirmed to function as a called number for callback; determination means for determining, when a call has been received from the extension terminal, whether or not the predetermined number is obtained, which corresponds to a connected party number received from the extension terminal or a connected party number corresponding to the extension number, with use of the information stored in the memory means; and means for employing, when the acquisition of the called number has been determined by the determination means, the predetermined number as a connected party number and transmitting response information including information relating to the connected party number to the communication network. It is preferable that the private branch exchange according to claim 1 further comprise means for sending a caller number presentation restriction to the communication network, when the determination means has determined that the predetermined number cannot be obtained, which corresponds to a caller number (connected party number) received from the extension terminal or a caller number (connected party number) corresponding to the extension number. With this structure, a caller number (connected party number), with which a callback can actually be made, can be informed to the counter-side terminal.
Preferred embodiments of the private branch exchange of the present invention are as follows:
(1) The memory means stores called number information as the predetermined number, and information for converting the called number information to a corresponding called party extension number or called number, and the determination means determines, when a call has been transmitted from the extension terminal (when the extension terminal has responded to a reception call), whether or not a called number is obtained, which corresponds to a caller number (a connected party number) received from the extension terminal or a caller number (a connected party number) corresponding to the extension number, with use of the information stored in the memory means. The private branch exchange further comprises means for sending a caller number (connected party number) presentation restriction to the communication network, when the determination means has determined that the called number cannot be obtained, which corresponds to a caller number (a connected party number) received from the extension terminal or a caller number (a connected party number) corresponding to the extension number. With this structure, an already provided memory means may be used without providing a new memory means, and this is practically advantageous.
(2) The memory means stores information relating to a caller number (a connected party number) permitted in the communication network as the predetermined number, and the determination means determines, when a call has been transmitted from the extension terminal (when the extension terminal has responded to a reception call), whether or not a caller number (a connected party number), which corresponds to a caller number received from the extension terminal or a caller number (a connected party number) corresponding to the extension number, is a caller number (a connected party number) permitted in the communication network, with use of the information stored in the memory means. The private branch exchange further comprises means for sending a caller number (connected party number) presentation restriction to the communication network, when the determination means has determined that the called number, which corresponds to a caller number (a connected party number) received from the extension terminal or a caller number (a connected party number) corresponding to the extension number, is not the permitted caller number (connected party number).
(3) In the above structure, at least an exclusive line is included, the determination means determines whether or not a called number, which corresponds to a caller number (a connected party number) received from the exclusive line or a caller number (a connected party number) corresponding to the exclusive line, can be obtained with respect to the caller number (connected party number) when a call is sent from the exclusive line to the communication network, and if the determination means has determined that the called number is obtained with the transmission means, the called number corresponding to a caller number (a connected party number) received from the extension terminal or a caller number (a connected party number) corresponding to the extension number is employed as the caller number (connected party number) and transmission call information including information relating to the caller number (connected party number) is transmitted to the communication network. Since the means for informing the caller number or connected party number is provided, it is possible to positively inform a caller number presentation restriction to the network, thereby preventing the network from supplementing a caller number which is invalid for the callback.
According to the present invention, it is possible with a simple structure to extract a caller number with which a callback can actually be made, and to prevent a caller number, with which a callback cannot be made, from being sent to the counter-side terminal in a case where the caller number permitting the callback cannot be extracted.
Moreover, according to the present invention, the following problem can be prevented: even in a case where caller numbers positively associated with extension numbers are transmitted to the network, if an office line different from an ordinary one is selected by an office line select function of the private branch exchange, a caller number which is correct on an ordinarily used office line may be restricted by a network verification function, or if a caller number is supplemented by the network and received by the counter-side terminal, a caller number which is unavailable for callback may be transmitted.
In a private branch exchange including at least a public line and having a function of interconnecting public lines automatically or manually, a caller number presentation restriction may be sent to a public line performing out-connection, irrespective of the presence/absence and content of a caller number received from an in-connection side public line, or when a public line performing out-connection has responded a reception call, a connected party number presentation restriction is sent to an in-connection side public line, irrespective of the presence/absence and content of a connected party number received from the public line. In this case, presentation of all caller numbers (connected party numbers) is restricted. Thus, in this case, too, the problem in which the caller number unavailable for callback is erroneously transmitted can be prevented, as in the above case.